Well, technically, a sus chord actually substitutes the 3rd with either the 4th or the 2nd; whereas an add9 adds the 9th to the major chord.

So a Csus2 would be: C-D-G (the E is omitted)
A Csus4 (often shown just as Csus) would be: C-F-G (the E is omitted)
A Cadd9 would be: C-E-G-D
And a C9 is actually an extension of C7, so it would b: C-E-G-Bb-D

BIAB supports the sus designation and implements it as a sus4.

BIAB also supports the add9, but implements it as a 2 (you would enter C2), in which the 2 may or may not be in the correct octave. That may or may not matter in a band (versus a single instrument) setting, depending on which instrument(s) play the 2. So sometimes you get C-D-E-G and sometimes you get C-E-G-D (and possibly C-E-G-C-D, depending upon the style).

BIAB also support the 9 designation properly: C9 = C-E-G-Bb-D

I guess that makes it clear as mud.

I wish BIAB would allow for the "add9" designation, and implemented it in the correct octave. I wouldn't think that would be too difficult to parse from the entered chord. If you want the close harmony, then it should also allow for an "add2", which is different than a "sus2". You see these an awful lot in music notation.

Likewise, I also see a lot of "no3". It would be nice to have that supported as well. Technically "C5" omits the 3, but not all styles do that. "No3" explicitly says don't play the 3, versus implies it.

My $0.02 worth.

John

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